Since platelet was discovered in 1842 by Donne, platelet has been considered as one blood component required for hemostasis for a long time. Presently, it is demonstrated that platelet not only just plays a principle role in the hemostatic mechanism but also exerts multi-functionality for example in the establishment of arteriosclerosis having been drawing clinical attention and the involvement in circulatory diseases including thrombotic diseases, cancer metastasis, inflammations, and post-graft rejections, and additionally in immune reactions.
Generally, therapies for blood reperfusion with pharmaceutical agents or physical methods have been done for thrombotic diseases and ischemic diseases. However, it has been found in recent years that phenomena such as the elevation of platelet activation, adhesion and aggregation occur after blood reperfusion, for example via the rupture of vascular tissues including endothelial cells or the deterioration of the balance between fibrinogenolysis and coagulation with pharmaceutical agents themselves. Clinically, such phenomena have drawn attention. It has also been revealed that after reperfusion is established with thrombolysis using for example t-PA, fibrinolysis potency and coagulation potency are activated, leading to the deterioration of the balance between systemic coagulation and fibrinolysis. Clinically, such phenomena induce re-occlusion and cause serious clinical problems (non-patent reference 1).
Meanwhile, PTCA and stenting have spread rapidly for the therapeutic treatment of diseases based on the constrictions of coronary artery and aorta, including for example angina and myocardial infarction, to give certain fruitful results. However, these therapies disadvantageously damage vascular tissues including endothelial cells, so that acute coronary occlusion and restenosis emerging at chronic stage draw serious concerns. Platelet plays an important role in various thrombotic disorders (re-occlusion and the like) after blood reperfusion therapy. Therefore, anti-platelet agents efficacious in these cases are now desired. However, anti-platelet agents in the related art have not yet been verified to be sufficiently effective.
As the prophylactic or therapeutic agents of these circulatory diseases, platelet aggregation inhibitors such as aspirin, indometacin, cilostazol, prostaglandin I2, prostaglandin E1, ticlopidine, and dipyridamole have been used. Recently, GPIIb/IIIa antagonists inhibiting the final stage of platelet aggregation and having a potent platelet aggregation-inhibiting activity has additionally been developed. The application thereof is however limited to intravenous infusion at the acute stage of thrombosis (non-patent reference 2).
It has been elucidated in recent years concerning ticlopidine for use as an anti-platelet agent that an active metabolite thereof can exert its platelet aggregation-inhibiting action by inhibiting P2Y12 as an ADP receptor. Reports have subsequently been issued, telling triazolo[4,5-D]pyrimidine derivative (patent reference 1) and piperidine and/or homopiperazine (patent reference 2 and patent reference 3) as compounds with the P2Y12-inhibiting action.
Anti-microbial compounds represented by the formula (A) have been known as quinolone derivatives (patent reference 4). However, it has never been known that these derivatives have a platelet aggregation-inhibiting action.
(See the official gazette of the patent reference 4 about the symbols in the formula.)
[Non-patent reference 1] Journal of the American College of Cardiology, 1988, Vol. 12, p. 616-623
[Non-patent reference 2] General Clinical Practice (“Sogo Rinsho” in Japanese), 2003, Vol. 52, p. 1516-1521
[Patent reference 1] The pamphlet of International Publication WO 00/34283
[Patent reference 2] The pamphlet of International Publication WO 02/098856
[Patent reference 3] The pamphlet of International Publication WO 03/022214
[Patent reference 4] The pamphlet of International Publication WO 98/23592